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801.
In this paper the 0-1 combined BEM is adopted to subdivide the computational domain boundary,and to discretize the Green’s integral expression based on Laplace equation.The FEM is used to subdivide the wave surface and deduce the surface equation which satisfies the nonlinear boundary conditions on the surface.The equations with potential function and wave surface height as an unknown quantity by application of Taylor expansion approach can be solved by iteration within the time step.In m-time iteration within the computational process of time step(n-1)Δt to nΔt,the results of the previous iteration are taken as the initial value of the two-order unknown terms in the present iteration.Thus,an improved tracking mode of nonlinear wave surface is established,and numerical results of wave tank test indicate that this mode is improved obviously and is more precise than the previous numerical model which ignored the two-order unknown terms of wave surface location and velocity potential function in comparison with the theoretical values. 相似文献
802.
《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(8):875-884
An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site of the ANTARES neutrino telescope near Toulon, France, thus providing a unique opportunity to compare high-resolution acoustic and optical observations between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward vertical currents of magnitudes up to 0.03 m s−1 in late winter and early spring 2006. In the same period, observations were made of enhanced levels of acoustic reflection, interpreted as suspended particles including zooplankton, by a factor of about 10 and of horizontal currents reaching 0.35 m s−1. These observations coincided with high light levels detected by the telescope, interpreted as increased bioluminescence. During winter 2006 deep dense-water formation occurred in the Ligurian subbasin, thus providing a possible explanation for these observations. However, the 10-20 days quasi-periodic episodes of high levels of acoustic reflection, light and large vertical currents continuing into the summer are not direct evidence of this process. It is hypothesized that the main process allowing for suspended material to be moved vertically later in the year is local advection, linked with topographic boundary current instabilities along the rim of the ‘Northern Current’. 相似文献
803.
J. Clodman 《大气与海洋》2013,51(1):1-7
Although an official observatory was established in Toronto in 1839, governmental attempts to organize a national meteorological service were not begun until 1871. Storm warnings and general weather forecasts for Eastern Canada were instituted in 1876, and this service was extended across the West and throughout the settled portions of the country by the early years of the 20th century. Historical climatological data were published annually after 1871, but very little statistical data, delineating the climate of the country, were available prior to 1900. A beginning was made at expanding meteorological activities into the North before World War I, but it was not until the 1920's that a significant number of observing stations were located there. By 1930 the need for extensive aviation meteorological services was becoming apparent, but the economic depression prevented an expansion of both aviation and meteorological services. 相似文献
804.
The GeV-TeVγ-ray line signal is the smoking gun signature of dark matter annihilation or decay.The detection of such a signal is one of the main targets of some space-based telescopes,including Fermi-LAT and the upcoming missions CALET,DAMPE and Gamma-400.An important feature ofγ-ray line photons that originate from dark-matter-annihilation is that they are concentrated at the center of the Galaxy.So far,no reliableγ-ray line has been detected by Fermi-LAT,and the upper limits on the cross section of annihilation intoγ-rays have been reported.We use these upper limits to estimate the"maximal"number ofγ-ray line photons detectable for FermiLAT,DAMPE and Gamma-400,and then investigate the spatial distribution of these photons.We show that the center of the distribution will usually be offset from the Galactic center(Sgr A)due to the limited statistics.Such a result is almost independent of models of the dark matter distribution,and will render the reconstruction of the dark matter distribution with theγ-ray line signal very challenging for foreseeable space-based detectors. 相似文献
805.
Dynamical features of the East Greenland Current (EGC) are synthesized from a survey conducted by the Swedish icebreaker Oden during the International Arctic Ocean - 02 expedition (AO-02) in May 2002 with emphasis on the liquid freshwater transport and Polar Surface Water. The data include hydrography and lowered acoustic doppler current profiler (LADCP) velocities in eight transects along the EGC, from the Fram Strait in the north to the Denmark Strait in the south. The survey reveals a strong confinement of the low-salinity polar water in the EGC to the continental slope/shelf—a feature of relevance for the stability of the thermohaline circulation in the Arctic Mediterranean. The southward transport of liquid freshwater in the EGC was found to vary considerably between the sections, ranging between 0.01 and 0.1 Sverdrup. Computations based on geostrophic as well as LADCP velocities give a section-averaged southward freshwater transport of 0.06 Sverdrup in the EGC during May 2002. Furthermore, Oden data suggest that the liquid freshwater transport was as large north of the Fram Strait as it was south of the Denmark Strait. 相似文献
806.
The polarimetric radar network in Jiangsu Province has just been operationalized since 2020. The first intense precipitation event observed by this polarimetric radar network and disdrometer occurred during August 28-29, 2020 and caused severe flooding and serious damage in eastern Jiangsu Province. The microphysics and kinetics for this heavy precipitation convective storm is diagnosed in this study, in order to promote the application of this polarimetric radar network. Drop size distribution(... 相似文献
807.
808.
Life cycle of intraseasonal oscillation of summer SST in the western South China Sea 总被引:1,自引:0,他引:1
Intraseasonal oscillation (ISO, times-cales of 30~90 d) of summer sea surface temperature (SST) in the western South China Sea is studied using harmonic and empirical orthogonal function analyses of microwave observations by the tropical rainfall measuring mission satellite. Each summer from May to September, two or three ISO events occur off South Vietnam, with a typical period of approximately 50 d. The life cycle of these events from the initiation to decay of SST anomalies is described. 相似文献
809.
针对传统方法采用天气雷达进行强降水的定量估测存在较大偏差问题,论文以1 h累计雨量为估测对象,基于雷达组网拼图资料,采用XGBoost(eXtreme Gradient Boosting)算法,建立新的雷达估测降水模型。该模型设计以前1 h的雷达组合反射率因子作为输入,进一步采用若干个剔除异常样本的策略有效清除建模样本中的部分噪声,更好地构建了雷达组合反射率与估测对象之间的非线性映射关系。在32万个独立检验样本的估测结果中,其均方根误差(RMSE)为6.04 mm、平均绝对误差(MAE)为3.50 mm、预报偏差(BIAS)为1.05;与目前业务系统上使用的ZR(300,1.4)关系方法相比,前者的RMSE和MAE分别下降了20.6%和10.3%,而BIAS指标则显示后者对降水量级的估测明显低估。进一步对小时雨强大于10 mm样本的统计结果表明,新方案的RMSE、MAE以及TS评分均大幅优于ZR(300,1.4)关系方法,可进行实际业务应用。 相似文献
810.